Establishing a Cover Crop

October 21, 2009

Author: Neighborhood Farm Initiative

Autumn is now upon us, and with it comes the end of the growing season for the many vegetables and herbs grown this year in our garden. But while the cooler weather marks the end of the vegetables, it also signals the beginning of another important phase in the development of our garden. One of the greatest challenges faced by organic farmers and gardeners alike is providing and maintaining adequate nutrient levels in their soil without the use of conventional fertilizers. The use of winter cover crops is one simple and effective way to add nutrients, while maintaining the complex soil ecosystem we’ve worked so hard to develop.

Cover crops, which can also be referred to as green manure crops, are traditionally sown at the end of the growing season. They provide numerous benefits including increasing available nutrients, increasing water holding capacity, suppressing the growth of weeds, controlling erosion, providing a habitat for beneficial insects, and breaking disease cycles. The cover crop will grow over the winter and then be incorporated into the soil prior to planting in the spring.

When spring rolls around and we begin to sow our crops for the new year, their roots will begin to penetrate the soil in search of vital nutrients. Most notably, nitrogen. Nitrogen is essential in the formation of amino acids, which are the building blocks of all living organisms. While nitrogen is in abundance in our atmosphere, in fact it is the largest single constituent(~75%) of our atmosphere, this form of nitrogen is not usable by plants or animals. Fortunately we are able to gain access to this reserve through the use of plants which convert or “fix” atmospheric nitrogen into plant available forms. Instead of applying an outside source of nitrogen come springtime, our cover crop will be working throughout the winter to store nitrogen for our crops in the spring. Then when we incorporate the cover crop into the soil in the spring, the plants will begin to decompose, releasing more nitrogen and other important nutrients into the soil.

Aside from providing vital nutrients, the cover crop will also help maintain the soil that we already have. If we were to leave the garden bare for the entire winter our soil would be exposed to the elements for many months. Rain, snow and wind would slowly wash away the most nutrient rich portions of the soil. The foliage and roots of the cover crop will keep hold of our soil and make sure those vital nutrients remain in our garden.

This year we chose to use a mixture of four crops; Bell Bean, Winter Pea, Vetch and Oats. The first three fall into the nitrogen fixing category, and they constituted about 90% of the mix. While the oats do not provide any nitrogen fixation, they provide a wide, fibrous root base which will be essential in preventing erosion. To establish the cover crop we first had to remove the dead plants and weeds and transfer them to our composting heaps. Then in each row we plowed three smaller rows and lightly seeded the cover crop by hand.